Clinical Endodontics

BioRaCe—Efficient, safe and biological based sequence files

by Gilberto Debelian & Martin Trope, USA

Endodontics is the prevention or elimination of apical periodontitis. Apical periodontitis is caused by microbes in a necrotic pulp.1-3 If the pulp is vital, apical periodontitis of endodontic origin is not possible.4,5 Vital pulp therapy (operative dentistry or root treatment of a vital pulp) is considered prevention of apical periodontitis while the disinfection steps when treating a necrotic infected pulp is considered elimination of apical periodontitis.

Phases of endodontic therapy

The root canal therapy comprises two phases:

1. The microbial control phase—the aim of this step is to avoid (vital pulp) or eliminate (necrotic/infected pulp) as many microbes as possible before moving to the next step.

2. Root filling phase—the 'clean and/or disinfected' canal is sealed so that an environment is in place to heal a previous apical periodontitis or maintain a healthy periodontium apically.

As mentioned above, the microbial control phase of root treatment is aimed at leaving as few microbes as possible in the canal before filling. It is irrefutable that less microbes at the time of filling results in more success of the treatment.6–11

In fact, if a technique is used that ensures that microbes cannot be cultured before filling the canal, an extremely high success (>90%) should be expected (Fig. 1).6–11 Therefore every step in the microbial control phase of root treatment is designed to remove additional microbes from the root canal. The microbial control phase comprises mechanical instrumentation, irrigation, root canal medication (when required) and to a small extent the root filling also (Fig. 2).

This paper will concentrate on the mechanical instrumentation and its effect on controlling intracanal infection. Specially, attention will be given to a new NiTi rotary sequence—BioRaCe.

Mechanical instrumentation is a critical step in the prevention/disinfection of the root canal. Studies have shown that even when no biologically active irrigating solution is used, that as the canal is instrumented to larger diameters so the number of remaining microbes is significantly reduced.12–15 However, a dilemma exists in that the natural sizes of the apical third of almost all root canals are surprisingly large.16–19 One example is shown in the study by Green (Fig. 3).16

Studies have been performed as to how large a canal should be instrumented in order to adequately clean (and thus disinfect) most root canals.20,21 The chart below is what is recommended as minimal sizes in order to have the best chance of cleaning the root canal (Fig. 4).

As is appreciated, these sizes are considerably larger than what is achieved by using the traditional step-back shape of instrumentation. However, as can now be appreciated when comparing the apical sizes of #25, #30 of the step-back shape to the natural sizes of the canal, that the step-back shape has little chance of removing canal microbes and relies almost entirely on irrigating solutions and intra-canal medications for disinfection and thus success of treatment. Conclusive evidence exists showing that the step-back sizes are insufficient to clean most canals (Fig. 5).12,22,23

An additional problem of using minimal apical instrumentation sizes and irrigating solutions is that the effectiveness of these solutions is 'neutralized' when the apical third of the canal is instrumented to smaller sizes. Research has shown that the medicaments cannot reach the apical third of the canal unless minimal sizes larger than those provided by the step-back shape produce (Fig. 6).22
The nickel titanium file 'revolution' has been accompanied by many other innovations in root canal instrumentation. Included are files of different taper and different cutting length. With stainless steel files, canals were instrumented exclusively in apex to orifice shaping technique. This resulted in a large amount of apical dentinal debris, blocking and ledging of canals. With the advent of NiTi files, the crown-down technique using large tapered instruments has become the standard. Thus instruments with relatively larger tapers and moved from the orifice to the apex in a step wise fashion. This has eliminated apical dentinal debris as a major problem since the apex is the last segment of the canal to be instrumented.

However the crown-down technique with large tapered files created another challenge. It is not possible to enlarge the apical third of the canal to biological sizes with large tapered instruments since the coronal half of the canal would be grossly over prepared if the apical sizes were correct.

Until the BioRace sequence (FKG Dentaire) was introduced, the practitioner had to chose between a step-back apical preparation (inferior cleaning and relying on irrigation) or the other alternative which is to use two sets of files, the first set is to reach the apical third with decreasing tapered instruments (crown-down fashion) and then a second set of files with a lesser taper in order to adequately clean the critical apical third of the canal (apical enlargement). Research has shown that the use of two sets of files with a hybrid technique is superior to the step-back alternative and in fact can in many cases with adequate adjuncts consistently render the canals culture negative.20 However, since a second set of files is required adding additional time and expense to the procedure, most manufacturers promote step-back canal shapes since fewer instruments are required and thus they are more attractive to the dentist who is also used to preparing canals to this shape.

The BioRaCe sequence uses our knowledge of the natural sizes of canals in order to minimize the number of files (one set of files) required to both adequately crown-down and enlarge apically without undue stress of each file.

BioRaCe

BioRaCe instruments possess the same physical characteristics of the well known NiTi rotary RaCe instruments24–26 with, a) alternating cutting edges, b) non-cutting safety tips, c) sharp cutting edges (triangular section) without radial lands, and d) electro-chemical surface treatment. Bio RaCe differs from standard RaCe instruments in regard to instruments tapers, sizes, sequence and handle codes. The major goal of Bio RaCe is to achieve apical preparation sizes efficiently and safely that with the addition of antimicrobial irrigation will effectively disinfect the canal. The unique aspect of this sequence is that the apical sizes of most of the teeth can be achieved with only five to seven instruments (depending of the root canal anatomy – consult Fig. 4).

BioRaCe sets and instruments

BioRaCe has two sets of instruments, Basic and Extended. The Basic set contains six instruments (BR0-25/0.08, BR1-15/0.05, BR2-25/0.04, BR3-25/0.06, BR4-35/0.04 and BR5-40/0.04) and is recommended to use on the majority of the root canal anatomies (Fig. 7).

The unique aspect of this sequence is that the areas of contact of each file are such as to minimize stress on the files so that they can be safely used at full working length. (Fig. 8 shows the contact areas of each file on dentinal wall.)

Clinical protocol for BioRaCe basic set

A #10, and #15 K-file should be used on each canal until the #15 K-file can be placed to length with minimal pressure. The BR0 (#25/0.08/19 mm) is then used in the coronal aspect of the canal with 4 steady strokes. As can be seen from Figure 8, about 4 mm of the file will contact the canal in the most coronal part and the tip will work freely. The #15 K-file should then be used again to confirm that the pathway to the apical part of the canal could easily be achieved. BR1 (#15/0.05) follows and since a #15 file has already been used, the contact area for BR1 will be in the middle aspect of the file only. BR2 (#25/0.04 taper) contacts mostly the apical part of the canal since the previous file was a 0.05 taper file. BR3 (#25/0.06) has the same tip size as BR2 but a larger taper. Thus the contact area moved again to the coronal/middle aspect of the canal and the tip of this instrument will work freely. BR4 (#35/0.04) and BR5 (#40/0.04) are files with smaller tapers than BR3 and so they will cut only in the apical third thus getting to biological sizes safely. It is important to understand that apart from BR0 ALL instruments are used to working length. (The entire protocol with the BioRaCe basic set is shown in Fig. 9.)

Figs. 5–12: Longitudinal section of mesial root of mandibular molar. Files superimposed. (Image courtesy Dr Richard Walton) (Fig. 5). Reduction of bacteria with increased instrumentation sizes using saline (red) or sodium hypochlorite (blue) irrigation. Only between size #25 to #35 does the use of sodium hypochlorite help decrease the number of bacteria. Apparently, until size #25, not enough space is available for the disinfectant to reach the apical third.22 (Fig. 6) BioRaCe basic set (Fig. 7). Zones of contact on the dentinal walls. The green zones show where dentin is removed in a small amount, and the red zones are where the dentin is removed in greater amount. The areas where the red-green zones are not marked are the areas where the instrument does not enlarge the canal (green arrows). The white arrows show that the instruments are carried out to full working length but in fact are performing a crown-down technique (Fig. 8). Clinical protocol of BioRaCe basic set (Fig. 9). BioRaCe extended set (Fig. 10). Clinical protocol of BioRaCe extended set (Fig. 11). BioRaCe coding system (Fig. 12).

BioRaCe extended set and clinical protocol

The extended set contains four instruments, in which two instruments are dedicated to severe curved root canal anatomies (BR4C and BR5C) and two additional instruments to large root canal anatomies (BR7 and BR8) (Fig. 10). BR4C and BR5C are #35 and #40 respectively with 0.02 taper. These files are used when BR3 (#25, 0.06) in the basic set has difficulty getting to working length (normally, no more than a double repetition of 4 steady insertions). This is an indication that the 0.04 files in the basic set would be unduly stressed to get to working length. In these cases the files BR4C and BR5C are used since they have 0.02 taper, and these files will get to working length with less stress. BR6 is #50/0.04 and BR7 is a #60/0.02 are used in those canals where BR5 (#40/0.04) is not large enough to get to biological sizes (consult Fig. 4). The clinical protocol involving the instruments on the extended set is shown (Fig. 11).

The alternating sequence of sizes and tapers of the BioRaCe system has allowed the required apical sizes to be achieved without increasing the number of instruments. This is achieved because unlike other standard NiTi rotary systems (increase the apical sizes by 0.05mm— #15, #20, #25, #30, etc.), the BioRaCe does not progress in a uniform sequential fashion. Thus unnecessary stress on the tip of the instruments is avoided even at full working length. However because of the different tapers and tip sizes of the instruments, contact points (and thus stress) on the files is minimized, thus maintaining the safety of this sequence. Since this sequence alternates between sizes and taper in a nonsequential fashion, the coding system used for BioRaCe is based on coding bars (Fig. 12).

BioRaCe clinical cases

Case 1

Tooth 26 with the diagnosis of symptomatic pulpitis. A pulpectomy was carried out with BioRaCe instruments with copious irrigation of 1% NaOCL. The MB1 and MB2 canals were instrumented at 21.5 mm to size 35/0.04 (BR4), the DB canal at 21.0 mm to 40/0.04 (BR5) and the P canal at 22.0 mm to 60/0.02 (BR7). The final irrigation was done with 17% EDTA together with 30 sec of ultrasonication in each canal. The obturation was carried out with a thermoplastic technic (System B and Obtura) with Resilon points, cartridges and sealer.

Case 2

Tooth 47 with the diagnosis of symptomatic pulpitis. A pulpectomy was carried out with BioRaCe instruments with copious irrigation of 1% NaOCL. The MB and ML canals were instrumented at 22.5 mm to size 40/0.04 (BR5), the D canal at 22.0 mm to 60/0.02 (BR7). The final irrigation was done with 17% EDTA together with 30 sec of ultrasonication in each canal. The obturation was carried out with Resilon points and sealer with a lateral condensation technique.

Case 3

Tooth 46 with the diagnosis of asymptomatic apical periodontitis. A treatment of a necrotic pulp was carried out with BioRaCe instruments together with copious irrigation of 1% NaOCl. The MB and ML canals were instrumented at 19.5 mm to size 35/0.04 (BR4). The DB and DL canals at 18.5 mm to 50/0.04 (BR6). The final irrigation was done with 17% EDTA together with ultrasonication (30 sec per canal). The canals were dried and then irrigated with 2% chlorhexidine before a past of Ca(OH)2 was placed with the help of a lentulo bur inside the canals. Three weeks after, the patient came in asymptomatic. Ca(OH)2 paste was removed with EDTA and ultrasonication. The obturation was carried out with a cold lateral condensation technique with Resilon points and sealer.

Case 4

Tooth 17 with the diagnosis of symptomatic pulpitis. A pulpectomy was carried out with BioRaCe instruments with copious irrigation of 1% NaOCL. The MB1 and MB2 (which merged coronally at 3 mm) canals were instrumented (Bio RaCe extended set instruments) at 19 mm to size 35/0.02 (BR4C), the DB canal at 18.5 mm to 35/0.04 (BR4) and the P canal at 22.0 mm to 50/0.04 (BR6). The final irrigation was done with 17% EDTA together with 30 sec of ultrasonication in each canal. The obturation was carried out with a cold lateral condensation technique with Resilon points and sealer.

Case 5

Tooth 17 with the diagnosis of asymptomatic apical periodontitis. A treatment of a necrotic pulp was carried out with BioRaCe instruments together with copious irrigation of 1% NaOCl. The MB canal was instrumented at 19.5 mm to size 40/0.04 (BR5). The DB 21 mm to 40/0.04 (BR5), the P canal 21.5 mm to 50/0.04, (BR6). The final irrigation was done with 17% EDTA together with ultrasonication (30 sec per canal). The canals were dried and then irrigated with 2% chlorhexidine before a past of Ca(OH)2 was placed with the help of a lentulo spiral inside the canals. One week after, the patient came in asymptomatic. Ca(OH)2 paste was removed with EDTA and ultrasonication. The obturation was carried out with a cold lateral condensation technique with Resilon points and sealer.

Summary

The BioRaCe system combines efficiency and safety with the biological requirements for a successful endodontic outcome. If used with traditional instrumentation adjuncts like bioactive irrigating solutions, the dentist can expect optimal endodontic outcomes while not requiring additional files or time to adequately clean the apical third of the canal.

Editorial note: A complete list of references is available from the publisher. This article was originally published in Endo Tribune US, Vol. 3, Issue 3, 2008.